This invention relates to a rolling bearing with a rotation sensor having a detection element for detecting the number of revolutions or the rotating angle of an output shaft of an engine or a rotary shaft of a motor, the detection element being mounted on an electric circuit board having flexibility. It also relates to a rolling bearing with a rotation sensor characterized in the binder for the magnetic material of a magnetic encoder used therein.
As a method of detecting the number of revolutions and rotating angle, a method is known in which changes in magnetism with the rotation of a rotating element magnetized multipolarily on a ferromagnetic film around a rotary drum are detected by a detecting element and output as pulse signals.
Heretofore, if such a rotation sensor is mounted to a rolling bearing comprising, as shown in FIGS. 10A and 10B, an inner ring 2, an outer ring 3 and rolling elements 4, a rotating element 13 magnetized in multiple poles is mounted on the diametrically outer surface of the inner ring 2 which is a rotating bearing ring. An annular sensor housing 16 comprising, as shown in FIG. 11A in section, a peripheral wall 16a and a flange 16b extending inwardly is fixed to a core metal 5 fitted on the diametrically inner surface of the outer ring 3 which is a fixed bearing ring. The annular sensor housing 16 is formed with a groove 17 having such a section as shown in FIG. 11B. An electric circuit board 18 made of a glass fiber-containing epoxy resin which is superior in insulating performance and strength and has a thickness of about 1 mm is fitted in the groove 17 and mounted to the flange 16b. A detection element 9 is mounted on the electric circuit board 18 so as to be fitted on the inner peripheral surface of the peripheral wall 16a formed with the groove 17. Then, an electronic circuit part 10 is mounted on the surface of the board 18.
In this way, the rotation sensor comprising the rotating element 13 magnetized in multiple poles and the detection element 9 for detecting any change in magnetism due to the rotation of the former is mounted on the rolling bearing.
But as shown in FIGS. 10A and 10B, if the electric circuit board 18 is mounted to the flange 16b of the sensor housing 16, there is a disadvantage that the axial length L4 tends to be long because the axial length of the peripheral wall 16a has to be sufficient to house the rotating element 13 and the sensor housing 16 has to contain the electronic circuit part 10 which is mounted on the electric circuit board 18.
In order to eliminate such a disadvantage, it is conceivable to mount the electric circuit board 18 on the inner peripheral surface of the peripheral wall 16a of the sensor housing 16. But while the electric circuit board 18 made of a glass fiber-containing epoxy resin is high in mechanical strength, it has low elasticity and is hard and easy to break. Thus it is impossible to mount it arcuately on the inner peripheral surface of the peripheral wall 16a. 
In order to mount the electric circuit board 18, which is made of an epoxy resin, on the inner peripheral surface of the peripheral wall 16a of the sensor housing 16 without cracking it, as shown in FIGS. 12A and 12B, it is necessary to split the electric circuit board 18 into split boards 18a. In order to mount the split boards 18a on the inner peripheral surface of the peripheral wall 16a of the sensor housing 16, it is necessary to form grooves 17a for receiving the split boards 18 in the inner peripheral surface and fix them in the respective grooves 17a. This is troublesome and incurs increase in manufacturing cost.
An object of this invention is therefore to provide a compact bearing with a rotation sensor by shortening the axial length of a housing needed for mounting the rotation sensor.
FIG. 13 shows another conventional rolling bearing with a rotation sensor. In this rolling bearing, the inner ring 2 is a rotating bearing ring. A core metal 102 is fitted on the inner ring 2. The core metal 102 includes a fixed portion 102a and a flange portion 102b. The fixed portion 102a is fitted on the outer peripheral surface of the inner ring 2. A magnetic encoder 101 is fixed to the outer peripheral surface of the flange portion 102b. The magnetic encoder 101 is made of a magnetic material (such as a ferrite) joined by a binder.
To the outer ring 3, which is a fixed bearing ring, an S-shaped core metal 5 for mounting a sensor housing 16 is fixed. The sensor housing 16 has a built-in sensor element 11 which detects change in magnetism of the magnetic encoder 101. Here, the sensing direction is radial.
As the binder for the magnetic encoder 101, generally, a thermoplastic resin such as polyamide (PA) and polyphenylene sulfide (PPS) or nitrile rubber (NBR) is used.
If a thermoplastic resin (plastic) is used for the binder for the magnetic encoder 101, the latter is molded simultaneously with the core metal 102 or pressed into or bonded to the core metal after molding.
But if a thermoplastic resin such as polyamide or polyphenylene sulfide is used for the binder for the magnetic material of the magnetic encoder 101, the magnetic accuracy of the magnetic encoder 101 may deteriorate if the bearing is left in a low-temperature or a high-temperature environment or in an environment where temperature fluctuations are repeated from high to low temperature over a wide temperature range (e.g. −40° C. to 130° C.).
Also, with a bearing in which the magnetic encoder 101 is pressed into the core metal 102 or the magnetic encoder 101 and the core metal 102 are simultaneously molded, cracks may develop during manufacture or if they are used in an environment in which temperature fluctuations are large.
If nitrile rubber is used as the binder, cracks may develop in an environment in which it is used at the upper limit of the above temperature range.
Thus, another object of the present invention is to provide a rolling bearing with a rotation sensor which can suppress deterioration of the magnetic accuracy even if left in a high-temperature or low-temperature environment or in an environment in which the temperature fluctuates repeatedly, and which can suppress cracks during manufacture or if used in an environment in which the temperature fluctuation is large or in a high-temperature environment.